Java代码对数组进行统计（使用方法），但有错误消息

Question

我对 Java 还很陌生。我目前正在参加入门课程，因此我在编写程序的过程中遇到了许多错误。当我尝试使用数组时，这段代码尤其存在问题。目标是计算并输出平均值、中值、最小值、最大值、范围和偏度。我们必须将文件保存在名为 silvestri 的包中，然后将其导入程序中以读取数字并执行上述所有数学函数。

第 57 行和第 70 行出现错误“表达式的类型必须是数组类型，但它解析为 int”

第 35 行有错误“此方法必须返回 double 类型的结果”和另一个错误消息“类型统计中的方法 range(double []) 从未在本地使用”

第 91 行有错误：“死代码”

它还输出两次平均值，但不输出我的任何其他 sytem.out.println////() 语句。我做错了什么？

这是我的代码：


import java.util.Arrays;
import java.util.Scanner;

import silvestri.DataStore;

public class Statistics {
    private final static String TITLE = "Statistics on an Array V1.0";
    private final static String CONTINUE_PROMPT = "Do this again? [y/N] ";
    
    //**********************************************
    // Put as many methods you need here
    private static double mean(double[] x) {
        if (x.length == 0) {
            return Double.NaN;`your text`
        }
        double sum = 0;
        
        for (int i = 0; i < x.length; i++)
            sum += x[i];
        double mean = sum / x.length;
        System.out.println("The mean is: " + mean);
        return mean;
        
    }

    private static double median (double[] x) {
        double median = 0;
        Arrays.sort(x);
        if (x.length % 2 != 0) {
            median = x[x.length / 2];
            System.out.println("The median is: " + median);
            return median;
        }
        else {
            median = (x[(x.length - 1) / 2] + x[x.length / 2]) / 2.0;
            System.out.println("The median is: " + median);
            return median;
        }
    }
    
    private static double maximum (double[] x) {
        double maximum = x[0];
        double minimum;
        
        for (int i = 1; i < x.length; i++) {
            if (x.length[i] > maximum) { 

/*error message: "the type of the expression must be an array type, 
  but it resolved to int" 
*/
                maximum = x[i];
            }
        }
        System.out.println("The maximum is: " + maximum);
        return maximum;
    }
    
    private static double minimum (double[] x) {
        double maximum = x[0];
        double minimum;
            for (int i = 1; i < x.length; i++) {
                if (x.length[i] < minimum) { 
/*error message: "the type of the expression must be an array type, 
  but it resolved to int" 
*/
                minimum = x[i];
                }
            }
            System.out.println("The minimum is: " + minimum);
        return minimum;
    }
    
    private static double range (double[] x) {

/* error message: the method range(double []) must return a result of 
   type double
*/
        //initializing maximum and minimum
        double maximum = x[0];
        double minimum = x[0];
        double range = 0;

            for (int i = 1; i < x.length; i++) {

// error message: dead code

                if (x[i] > maximum) {
                    maximum = x[i];
                }
                if (x[i] < minimum) {
                    minimum = x[i];
                }
            System.out.println("The range is: " + range);
            return range = maximum - minimum;
            }
        }
    https://stackoverflow.com/
        public static String skew (double[] x) {
            double sum = 0;
            double mean;
            double median = median(x);
            
            for (double num : x) {
                sum += num;
            }
            mean = sum / x.length;
            
            double difference  = Math.abs(mean-median);
            
                if (mean > median) {
                    return "The data is right skewed";
                }
                // checking if the absolute difference is within 10E-6
                else if (Math.abs(difference) < 10E-6) {
                    return "The data has no skew";
                }
                else {
                    System.out.println("The data is left skewed");
                }
            }
    
    //**********************************************
    // Start your logic coding in the process method
    private static void process(Scanner input, String args[]) throws Exception {
        double data[] = DataStore.getData();
        double mean = mean(data);
        // write a method called mean that's gonna pass the array doubles & it will return            average
        double ave = mean(data);
    }
    
    //**********************************************
    // Do not change the doThisAgain method
    private static boolean doThisAgain(Scanner input, String prompt) {
        System.out.print(prompt); 
        String doOver = input.nextLine();
        return doOver.trim().equalsIgnoreCase("Y");
    }
    
    //**********************************************
    // Do not change the main method
    public static void main(String args[]) throws Exception {
        System.out.println("Welcome to " + TITLE);
        Scanner input = new Scanner(System.in);
        do {
            process(input, args);
        } while (doThisAgain(input, CONTINUE_PROMPT));
        input.close();
        System.out.println("Thank you for using " + TITLE);
    }

}

我尝试修复数组、双精度和字符串变量。一些代码得到了改进，但在我尝试对代码进行故障排除后，上述行出现了问题。

Answer 1

从您问题中的代码：

if (x.length[i] > maximum) { 

/*error message: "the type of the expression must be an array type, 
  but it resolved to int" 
*/

计算机编程语言包含称为“表达式”的东西。表达式返回值。表达式

x[i] 返回数组 x

 中索引

i

 处的元素的值，例如

x[0]

 返回数组

x

 中的第一个元素。表达式

x.length

 返回数组

x

 中的元素数量。但是，没有

x.length[i]

 表达式，这就是您收到错误的原因。应该只是

x[i]

。

也来自您问题中的代码：

if (x[i] < minimum) { 
/*error message: "the type of the expression must be an array type, 
  but it resolved to int" 
*/

有时错误消息可能很神秘。这里的问题是你声明了变量

minimum

但没有初始化它。我指的是您的这行代码（在

if

 语句上方出现两行）：

double minimum;

我猜你希望这样：

double minimum = x[0];

下一个问题。

private static double range(double[] x) {

/* error message: the method range(double []) must return a result of 
   type double
*/

return

语句位于

for

循环内。请注意，数组可能包含零个元素，在这种情况下，

for

循环将不会被执行，这意味着该方法不会返回值。

return

语句位于

for

循环内这一事实也是导致

死代码

错误的原因。在

for 循环的第一次迭代中，将执行 return

 语句，因此循环将执行一次迭代，因此

i++

 永远不会被执行。

还有其他问题，但是如果您将下面的代码与您的代码进行比较，我相信您会发现它们是什么。

import java.util.Arrays;
import java.util.Scanner;

import silvestri.DataStore;

public class Statistics {
    private final static String TITLE = "Statistics on an Array V1.0";
    private final static String CONTINUE_PROMPT = "Do this again? [y/N] ";

    private static double mean(double[] x) {
        if (x.length == 0) {
            return Double.NaN;
        }
        double sum = 0;

        for (int i = 0; i < x.length; i++) {
            sum += x[i];
        }
        double mean = sum / x.length;
        System.out.println("The mean is: " + mean);
        return mean;
    }

    private static double median(double[] x) {
        double median = 0;
        Arrays.sort(x);
        if (x.length % 2 != 0) {
            median = x[x.length / 2];
            System.out.println("The median is: " + median);
            return median;
        }
        else {
            median = (x[(x.length - 1) / 2] + x[x.length / 2]) / 2.0;
            System.out.println("The median is: " + median);
            return median;
        }
    }

    private static double maximum(double[] x) {
        double maximum = x[0];
        for (int i = 1; i < x.length; i++) {
            if (x[i] > maximum) {
                maximum = x[i];
            }
        }
        System.out.println("The maximum is: " + maximum);
        return maximum;
    }

    private static double minimum(double[] x) {
        double minimum = x[0];
        for (int i = 1; i < x.length; i++) {
            if (x[i] < minimum) {
                minimum = x[i];
            }
        }
        System.out.println("The minimum is: " + minimum);
        return minimum;
    }

    private static double range(double[] x) {
        // initializing maximum and minimum
        double maximum = x[0];
        double minimum = x[0];

        for (int i = 1; i < x.length; i++) {
            if (x[i] > maximum) {
                maximum = x[i];
            }
            if (x[i] < minimum) {
                minimum = x[i];
            }
        }
        double range = maximum - minimum;
        System.out.println("The range is: " + range);
        return range;
    }

    public static String skew(double[] x) {
        double mean = mean(x);
        double median = median(x);
        double difference = Math.abs(mean - median);

        if (mean > median) {
            return "The data is right skewed";
        }
        // checking if the absolute difference is within 10E-6
        else if (Math.abs(difference) < 10E-6) {
            return "The data has no skew";
        }
        else {
            return "The data is left skewed";
        }
    }

    private static void process(Scanner input, String args[]) throws Exception {
        double data[] = DataStore.getData();
        mean(data);
        median(data);
        maximum(data);
        minimum(data);
        range(data);
        System.out.println(skew(data));
    }

    private static boolean doThisAgain(Scanner input, String prompt) {
        System.out.print(prompt);
        String doOver = input.nextLine();
        return doOver.trim().equalsIgnoreCase("Y");
    }

    public static void main(String args[]) throws Exception {
        System.out.println("Welcome to " + TITLE);
        Scanner input = new Scanner(System.in);
        do {
            process(input, args);
        } while (doThisAgain(input, CONTINUE_PROMPT));
        input.close();
        System.out.println("Thank you for using " + TITLE);
    }
}

当我使用以下数组运行上面的代码时

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

我得到以下输出

The mean is: 4.5
The median is: 4.5
The maximum is: 9.0
The minimum is: 0.0
The range is: 9.0
The mean is: 4.5
The median is: 4.5
The data has no skew
Do this again? [y/N] N
Thank you for using Statistics on an Array V1.0

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